Carbon chauvinism / REF / 131 / 2014

Carbon chauvinism is a neologism meant to disparage the assumption that the chemical processes of hypothetical extraterrestrial life must be constructed primarily from carbon (organic compounds) because carbon's chemical and thermodynamic properties render it far superior to all other elements.

Concept

The term was used as early as 1973, when scientist Carl Sagan described it and other human chauvinisms that limit imagination of possible extraterrestrial life. It suggests that human beings, as carbon-based life forms who have never encountered any life that has evolved outside the Earth’s environment, may find it difficult to envision radically different biochemistries.
In a 1999 Reason magazine article discussing the theory of a fine-tuned universe, Kenneth Silber quotes astrophysicist Victor J. Stenger using the term:
There is no good reason, says Stenger, to "assume that there's only one kind of life possible" - we know far too little about life in our own universe, let alone "other" universes, to reach such a conclusion. Stenger denounces as "carbon chauvinism" the assumption that life requires carbon; other chemical elements, such as silicon, can also form molecules of considerable complexity. Indeed, Stenger ventures, it is "molecular chauvinism" to assume that molecules are required at all; in a universe with different properties, atomic nuclei or other structures might assemble in totally unfamiliar ways.

Carbon alternatives

Like carbon, silicon can form four stable bonds with itself and other elements, and long chemical chains known as silane polymers, which are very similar to the hydrocarbons essential to life on Earth. Silicon is more reactive than carbon, which could make it optimal for extremely cold environments. However, silanes spontaneously burn in the presence of oxygen, so an oxygen atmosphere would be deadly to any silicon-based life, and water as a solvent would be equally deadly for the same reason. So, any environment with the potential for silicon-based life would have to be very cold, devoid of oxygen and water, but with another compatible solvent, such as liquid methane or a methyl compound to exhibit polymer activity.
Hydrocarbons and organic compounds are abundant in meteorites, comets, and interstellar clouds, while their silicon analogs have never been observed in nature. Silicon does, however, form complex one-, two- and three-dimensional polymers in which oxygen atoms form bridges between silicon atoms. These are termed silicates. They are both stable and abundant under terrestrial conditions, and have been proposed as a basis for a pre-organic form of evolution on Earth (see clay hypothesis).

Criticism

The main argument favoring that only carbon-based life exists is that there is currently no empirical data to support other forms, such as life based on silicon. The apparent lack of silane polymers and the abundance of carbon in meteorites would suggest that carbon-based life is much more probable than silicon-based life.

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